1. Field of the Invention
The present invention relates to pressure sensitive adhesives, coatings, and films formulated from plant-based materials.
2. Description of Related Art
Pressure sensitive adhesives (PSAs) are defined as adhesives having tacky or sticky functional groups that do not cure or dry under ambient conditions. They can be adhered to other surfaces using only light pressure, and do not require any light, heat, or water to activate the adhesive nature of the composition. PSAs are usually based on an elastomer (carrier) compounded with a suitable tackifier. Some PSAs are repositionable. In other words, they form only a temporary bond and can be removed and re-adhered without leaving behind a residue. Some PSAs are designed for repeated use and do not substantially lose their initial tackiness or adhesion capability even when stuck and unstuck from various surfaces. The ubiquitous Post-it® note is an example of a product using a PSA. PSAs find many uses, including surface protection films, masking tapes, bookmark and note papers, price marking labels, promotional graphics materials, as well as for biomedical applications (e.g., wound care dressings, electrodes, athletic tape, drug patches, etc.). PSA compositions can also be used to form transparent films and coatings. Commercially-available PSAs are commonly made from mainly petroleum-based or synthetic materials. A decrease in fossil resources has urged the development of sustainable materials using renewable feedstocks, including plant-based materials.
Flexible materials are also of great interest in research and development of advanced electronic devices, including flexible solar cells, semiconductors, and displays. Current PSAs have limited application for electronic devices. For example, acrylate and rubber-based PSAs have very low thermal stability including a low glass transition temperature, high melting point, and a large coefficient of thermal expansion. Also silicone-based PSAs avoid these drawbacks, they are typically too expensive in comparison. They are also not made of bio-based materials.
Sustainable materials are of great interest as a replacement for non-renewable fossil resources. Plant oils, including a broad range of oleo-chemicals from plant oils such as methyl oleates and glycerols, are a ready-to-use feedstock and are generally used as additives in coating, paint, lubricant and plastic industries. However, existing attempts to create bio-based PSAs do not yield a satisfactory product. For examples, many bio-based PSAs have long curing times, making them unsuitable for actual commercial use. Other bio-based PSAs only incorporate a small amount of plant-based materials and still rely on petroleum-based materials for the bulk of their compositions. Still further bio-based PSAs have inferior properties, including poor shear strength, tack, and/or peel strength. They also have poor shelf-life, again, limiting their use in an actual commercial setting. Thus, there remains a need in the art for improved PSAs, films, and coatings that use sustainable materials, but achieve properties comparable to existing commercial PSAs, films, and coatings formulated with synthetic ingredients.